To identify new therapeutic targets for Lyme disease prevention, we propose to analyze the roles of Borrelia burgdorferi gene products that are highly induced in ticks. B. burgdorferi thrives in nature through an intricate enzootic cycle involving small rodents and Ixodes ticks. Immature ticks acquire the pathogen from an infected host, transstadially maintain B. burgdorferi, and transmit it to naove hosts during a subsequent blood meal. We hypothesize that spirochete genes that are preferentially induced at specific stages of the microbial life cycle in ticks are important for sustaining the pathogen in nature. As many of these tick-induced spirochete proteins may also be exposed on the pathogen surface, B. burgdorferi transmission should be influenced by specific antibodies against them. We will develop this paradigm using the model B. burgdorferi genes bb0323, bb0246, bba62 and bba52, many of which are localized on the spirochete surface and are upregulated at specific times and in specific tissues in ticks. First, we will explore the effect of targeted mutagenesis of the genes on the spirochete life cycle to establish the relative importance of specific B. burgdorferi gene products and to identify potential targets for subsequent antibody-blocking studies. We will then focus on important spirochete genes and assess if antibodies directed against selected B. burgdorferi gene products interrupt the microbial life cycle and result in host immunoprotection. We will also assess functions of tick-induced spirochete proteins focusing on vector-pathogen interaction. The information will help clarify the adaptive strategies of a bacterium that persists in a diverse array of host and vector tissues, and may contribute new targets for the development of preventive measures for disruption of the spirochete life cycle. PUBLIC HEALTH RELEVANCE: 7. Lyme disease, the most prevalent vector-borne disease in the United States, is caused by Borrelia burgdorferi, which is maintained in nature through an intricate tick-rodent infection cycle. We propose to characterize the functional roles of B. burgdorferi gene products that are preferentially induced in ticks and are critical for pathogen persistence and transmission. This information will contribute to the development of new therapeutic targets for a Lyme disease vaccine.